Andrews E70 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews E70 fault code mean?
The E70 code on Andrews MAXXflo and CWH-series water heaters signals a lockout condition originating from the slave control board — the secondary electronic module that governs one of the unit's burner sections. Andrews appliances use a master/slave board architecture, and when the slave board detects an internal error (such as a corrupted parameter set, an analogue-to-digital circuit reading outside acceptable limits, or a reference measurement failure), it triggers a protective lockout and displays E70 alternating with the number of the affected burner module. The unit will not fire again until the root cause is addressed and a manual reset is performed. Unlike simple operational faults, E-series codes on Andrews equipment always require an underlying fault to be corrected before a reset will hold — repeated resets without a repair will not clear this code permanently.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Slave control PCB internal failure Common
The slave board itself has developed a hardware fault — often due to component ageing, electrical surge, or long-term heat stress inside the appliance casing. When the board's internal self-diagnostics detect a failure, it immediately locks out the associated burner module and raises E70. This is the most frequent finding when E70 persists after a reset attempt.
- Incorrect or corrupted parameters on the slave board Common
Andrews documentation specifically lists 'incorrect parameters programmed in the slave board' as a trigger for this control error class. This can happen after a power interruption during a firmware update, a failed board swap where parameters were not correctly transferred, or spontaneous memory corruption over time.
- Wiring or connector fault between master and slave boards Sometimes
Loose, corroded, or chafed wiring in the harness linking the master controller to the slave board can cause communication errors that the slave board interprets as an internal fault, generating E70. Vibration in commercial plant rooms and moisture ingress are common contributing factors.
- Analogue-to-digital (AD) circuit defect on the slave board Sometimes
The slave board contains an AD-conversion circuit used to read sensor inputs. If this circuit drifts out of range or develops a component-level fault, the board flags the integrity failure and locks out. This is effectively a sub-type of PCB failure but is sometimes recoverable with board-level repair rather than full replacement.
- Mains power quality issue Rare
Andrews technical documentation notes that a significant deviation from 50 Hz on the mains supply can destabilise board operation and provoke control lockout codes. Persistent voltage fluctuations or a poor earthing arrangement in the plant room can contribute to repeated E70 occurrences even after a board replacement if the supply issue is not addressed.
How to fix it
- Check whether other burner modules are still operating DIY safe
On multi-module Andrews units, the display alternates between 'E70' and a module number, identifying which burner section has locked out. Note this number — other modules may still be providing hot water at reduced capacity. This information will be useful to pass on to your engineer.
- Attempt a single controlled reset using the reset button DIY safe
Locate the reset button on the Andrews control panel. Press and hold as described in your unit's operating guide. The reset only clears the lockout for the affected burner module. If the fault returns immediately or within a short time, do not keep resetting — a recurring E70 indicates a persistent hardware or wiring fault that must be investigated professionally. Limit resets to no more than two or three attempts.
- Check that the mains power supply to the unit is stable DIY safe
Verify that the isolator switch is fully on and that no other electrical equipment on the same circuit is tripping. If you have access to a basic plug-in mains tester, check the supply socket. Report any known power quality issues (frequent trips, flickering lights) to your engineer, as these can contribute to repeated board faults.
- Do not open the casing or attempt internal inspection yourself Gas Safe engineer
Andrews water heaters are commercial-grade appliances with gas, high-voltage electrical, and pressurised water components inside the casing. Opening the unit without the correct authorisation and competence is both unsafe and, on gas-fired plant, a legal matter under Gas Safe regulations. All internal work must be carried out by a Gas Safe registered engineer with experience of commercial water heaters.
- Arrange for a Gas Safe registered engineer to inspect wiring and connections to the slave board Gas Safe engineer
A competent engineer will systematically check the wiring harness between the master and slave control boards, looking for loose Molex connectors, pin corrosion, damaged insulation, and signs of moisture ingress. On Andrews MAXXflo and CWH units, the control boards are housed in a dedicated electronics enclosure — the engineer will need the relevant Andrews technical documentation to navigate the board layout safely.
- Have the engineer test and, if necessary, replace the slave control PCB Gas Safe engineer
Using diagnostic equipment, the engineer will assess whether the slave board has failed internally or whether a parameter re-flash might resolve corrupted settings. In most persistent E70 cases, board replacement is required. Andrews specify that only genuine Andrews-compatible replacement parts should be fitted to maintain safety certification and warranty. After fitting, the board parameters must be correctly programmed before the unit is test-fired.
- Ensure full recommissioning and sign-off after any board replacement Gas Safe engineer
Following a slave board replacement on an Andrews commercial water heater, the unit must be recommissioned — including combustion analysis, flue integrity checks, and confirmation that all burner modules are operating within specification. The engineer should provide a commissioning record. If the appliance is under an Andrews service contract, contact Andrews directly on 0345 070 1056 before arranging an independent engineer visit.
Parts you may need
- Andrews slave control PCB (module-specific, MAXXflo/CWH series) · from £290
- Master-to-slave wiring harness/connector set · from £45
- Control board parameter programming interface/cable · from £60
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £300–£700, depending on the underlying cause.
Frequently asked questions
Can I reset an Andrews E70 fault code myself?
You can press the reset button on the control panel once or twice to attempt a reset — the Andrews system only resets the specific burner module shown on the display. However, Andrews documentation is clear that E-series codes require the underlying fault to be corrected before a reset will hold. If E70 returns after your reset attempts, further resets will not help and you should stop and call a Gas Safe engineer. The fault will not resolve itself.
Is E70 a gas leak or safety emergency?
No — E70 is an electronic control board fault rather than a gas, pressure, or combustion safety alert. The affected burner module has simply locked itself out as a precaution. There is no immediate danger associated with E70 in the way there would be with a carbon monoxide or gas leak alarm. That said, you should not attempt to bypass or ignore the lockout, and the unit needs professional attention before the affected module can be safely returned to service.
How much does it cost to fix an Andrews E70 fault in the UK?
Because Andrews MAXXflo and CWH appliances are commercial-grade units, repair costs are higher than for standard domestic boilers. Most E70 repairs involve engineer call-out, diagnosis, and slave board replacement, typically falling in the range of £300–£700 including parts and labour. The slave PCB itself generally costs £180–£400 depending on the specific model variant, with labour on top. In rare cases where a board is no longer available as a standalone part or where additional faults are found, costs can exceed this — your engineer should provide a written quote before starting work.
Why does my Andrews unit keep showing E70 even after I replace the PCB?
Recurring E70 after a board swap usually points to one of two issues: either the replacement board was not correctly programmed with the unit's parameters (a step that must be carried out with Andrews-specific tooling), or there is an underlying mains power quality problem — such as significant 50 Hz frequency deviation or poor earthing — that is stressing the new board in the same way it damaged the original. A good engineer will check the power supply quality and verify parameter programming as part of the recommissioning process.